Probing Question: How does anesthesia work?

October 25, 2007

Many inventions of the 19th century -- telephones, airplanes, phonographs -- have helped to shape the modern world. However, it could be argued that the 1846 discovery of effective surgical anesthesia holds a place of honor among the century's advances.

Prior to the advent of effective anesthetics, surgery was a desperate last resort that used crude and dangerous means (including large doses of opium or alcohol, or knocking a patient unconscious) to dull the patient's sensations. Today, whether it is a shot of novocaine at the dentist, a spinal or epidural during childbirth, deep sedation for a minor procedure or general anesthesia for major surgery, the use of effective anesthesia is a routine part of medical care.

Although most of us have experienced anesthesia, the general public has little understanding of what it is and how it works. According to Steve Kimatian, associate professor of anesthesiology and pediatrics in Penn State's College of Medicine, anesthesia is not a single entity, but rather a manipulation of several physiological functions of the body.

"In its most basic sense, you can say that anesthesia consists of four components: hypnosis, amnesia, analgesia and muscle relaxation," explained Kimatian.

These components -- which range from local anesthetic injections to regional anesthetics (such as spinal and epidural) to general anesthesia -- may be combined or used separately depending on the type of surgery and patients' needs.

While you may have thought you were "asleep" for that tonsillectomy as a teenager, technically you were in a state of deep hypnosis. When you finally woke up in the recovery room, you probably didn't remember anything about the surgery -- thanks to the effects of amnesia-inducing agents you were given.

But Kimatian explains that sedation and amnesia do not necessarily mean the same thing. You can be "asleep" during a procedure but afterwards remember hearing the voices of the doctors or you can also be "awake" during a procedure, speaking with the doctors, answering questions and following commands, but remember nothing.

Said Kimatian, although you don't remember having any pain during the surgery, that doesn't necessarily mean the pain wasn't there.

"A person can be sedated and appear to be asleep, they can be amnesic and not remember anything, but their body can still have a physiological response to a stimulus. Consider the tree falling in the forest analogy. If you had pain and you don't remember it, did you really have pain? From an anesthesiologist's standpoint, yes, because we have to address those physiologic changes that occur with response to stimulus."

In cases requiring regional anesthesia, how do anesthesiologists block sensation to specific body parts and not others?

Explained Kimatian, if we touch a hot stove, thermal receptors in our hand send an electrical signal to our spinal cord which signals our brain, and we react by experiencing pain and removing our hand from the stimulus. To make sure we don't feel the pain during a surgery or procedure, an anesthesiologist uses analgesics or local anesthetics to block the signal somewhere between the point of the stimulus and the brain.

"I could do a regional anesthetic selective to an individual finger, by just blocking the nerves of that digit, and you wouldn't know the finger was in pain," Kimatian said. "Or you can block all the nerves to the forearm so you wouldn't feel the pain there. You could block it at the shoulder. You could block it at the epidural space where the nerves enter into the spinal sac, or you can put the person completely to sleep and block it at the cerebral level." The art and science of anesthesia, said Kimatian, is knowing how to tailor both the technique and the dosage to the individual patient's needs. "Understanding the delicate balance between desired effects and undesired side effects requires a physician's in-depth knowledge of physiology and pharmacology," he added.

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2 comments

This "expertise" needs to be reviewed... Although we have come a long way from whiskey and a branding iron, that doesn't mean this area of science is pushing forward in the way that it desperately needs to.

The studies show that anesthesiologists kill people at an alarming rate even during "routine procedures". My personal opinion is that they are not studying or taking into account enough personalized variables relative to the patient or even humans in general (i.e. perhaps they should have a better grasp on how circadian rhythms would effect dosage).

Don't even get me started on the "one size fits all" dosages that get prescribed or purchased OTC... "Adults take 1 to 2" crapola - no way that an 95 pound 17 year old female and a 350 pound 30 year old male athlete would have a dosage delta of exactly 1 tablet - with no guidance as to which of the two people should take 2. Shouldn't the delta be more refined to at least the .25 of a tablet level with more guidance as to what profile of a person would lead to what dosage????

OTC products are relatively safe, as long as they are used inside their predetermined guidelines. however, the guidelines are determined for the typical person. i would say that neither of the two cases you presented (95lb 17 y/o girl, or the 350lb athlete) would be considered typical. obviously if there is a question regarding the effectiveness of the minimum or maximum dosage, depending on the situation, then a doctor or pharmacist consultation should be considered.

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